1. Field of the Invention
The present invention relates to a track counting device for counting the number of recording tracks on a record medium of optical disk apparatus. More particularly, the invention relates to a track counting device which counts the number of recording tracks crossed by a light pickup element, which is radially moving over a record medium with concentric guide grooves of recording tracks, based on a tracking error signal output from the light pickup unit.
2. Description of the Related Art
An example of optical disk apparatus is a direct read after write optical disk apparatus using a record medium on which concentric guide grooves of recording tracks are formed. In such an optical disk apparatus, a light pickup element radially moves over the record medium for record and reproduction of data thereof and generates a tracking error signal. The optical disk apparatus then counts the number of recording tracks which have been crossed by the light pickup element, based on the tracking error signal output from the light pickup element. A conventional example of such track counting device is shown in FIG. 7.
In FIG. 7, a tracking error signal Et (cf. (a) in FIG. 8) output from an unrepresented light pickup element is shaped by a wave shaping circuit 1 with respect to the zero level. The thus obtained signal Ec (cf. (b) in FIG. 8) is then led to a counter 2.
The counter 2 counts the number of rise edges of the signal Ec. The count number is sent to a downward element as a crossed track data Ct (cf. (c) in FIG. 8) representing the number of recording tracks which have been crossed by the light pickup element.
In the above constitution, the tracking error signal Et is so sinusoidal that the maximum amplitude is gained at a side edge of guide groove of recording track during the recording track crossing of light pickup element. The period of the sinusoidal signal corresponds to a time necessary for crossing one recording track.
The signal Ec takes the logic level H when the tracking error signal Et surpasses the zero level accordingly, whereby one rise edge appears for one recording track in the signal Ec.
Consequently, the number of rise edges in the signal Ec coincides with the number of crossed recording tracks, while the count of counter 2 also with the latter. Hence the crossed track data Ct can provide the number of recording tracks which have been crossed by the light pickup element.
The conventional device has, however, the following problems.
The recording tracks are divided into a number of sectors of determined data length, each of which is given header information such as a sector address to discriminate one from others.
The header information data is preliminarily recorded in the recording track. Mirror finished portion not to record effective data are given between the header information and a user's data area in the sector in order to adjust properties of signal processing means of reproduction system.
When the light pickup element passes such a mirror finished portion the level of tracking error signal Et remains unchanged as shown as PA in (a) of FIG. 8. This results in no appearance of rise edge in the signal Et, which in turn causes no count operation of the counter 2. Therefore, one of problems appears as noncoincidence between the value of crossed track data Ct and the number of actually crossed recording tracks.
Further, the recording of data in the record medium is effected by forming pits (small holes) therein. When a laser beam from the light pickup element crosses such a pit in the user's data recorded area, a reflection level of laser beam increases at the edge of pit due to the edge effect. Such influence on the tracking error signal Et is shown as PB in (a) of FIG. 8.
The signal Ec then has a rise edge at each point where the level of PB in Et exceeds the zero level, so that the counter 2 counts each of the rise edges. This also leads to noncoincidence between the crossed track data value Ct and the actually crossed recording track number.